just as you mentioned, before i replaced the striker bushing i had to slam the door, so the door would go in far enough that the striker would make the latch flip closed, the latches i.d. is the size of the bushing, and when the bushing is missing, it causes the latch to have slop on the striker bolt the thickness of both sides of the bushing and would allow the door to rattle in and out. after new strikers it would close by just pushing the door closed. i suppose, if you have good weatherstripping, the weatherstripping would try to keep the door pushed out, possibly enough to keep the striker and latch making contact and only rattle when your on washboard on a gravel road or in a bouncy situation, my weatherstripping was shot so it let the door latch rattle on the striker all the time.
when i bought my new felts, i ordered the weatherstripping and felts in a kit that had all weatherstripping for both doors, and it was a night and day difference, my rattle trap was no longer a rattle trap, but, then i could hear my leaf spring bushings squeaking, so i then put new poly bushings in the spring eyes....
then, i could slightly hear the exhaust pipe vibrating against the frame, i fixed that and it made the truck so much better to ride in, it no longer sounded like crap, i was amazed at how much difference these little things had such a large difference in the sound of the truck..it was so much of a difference, it didn't seem to be the same truck and my friends realized it right away when they would ride w/me after i had fixed all the annoying noises.